At Centerdale, about three miles west of Providence, Rhode Island, there occur quartz crystals showing an unusual number of forms. The rock in which they are found is a green schist, composed principally of bladed hornblende, somewhat altered to chlorite. There is an intrusive granite nearby, and pegmatite stringers and quartz veins from it cut the schist. The quartz crystals occur in small open cavities, and have doubtless been formed by hot solutions emanating from the granite. They are normally clear and colorless, but at times are more or less filled with tiny plates of chlorite, giving them a green color. Their complex form may be the result of the presence of so much chloritic material in the solutions from which they crystallized. All are right-handed, and twinned, as shown by repetition of trigonal pyramid faces on adjacent corners.

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